1. Field of the Invention
The present invention relates to a temperature compensated crystal oscillator and a method of manufacturing the oscillator, and more particularly to a temperature compensated crystal oscillator and a method of manufacturing the oscillator which is intended to achieve compactness of a product by making use of a bottom surface as an area for accommodating components.
2. Description of the Prior Art
A crystal oscillator employing a quartz oscillator is an essential component used to generate an oscillation frequency for controlling transmission and reception of signals between mobile communication terminals, and is superior to other oscillators in terms of frequency stability. However, the quartz oscillator has a drawback in that its oscillation frequency varies depending on ambient temperature. To overcome this drawback, the crystal oscillator must be additionally provided with certain components for compensating frequency variation owing to temperature characteristics of the quartz oscillator. Such a crystal oscillator is referred to as a temperature compensated crystal oscillator (TCXO).
In general, a temperature compensating circuit of the TCXO comprises a temperature detection circuit employing resistance variation of a thermistor, a controlled voltage generating circuit for controlling a voltage according to the resistance variation, and a frequency adjusting circuit for adjusting frequency by capacitance regulation according to the controlled voltage. According to presence of the temperature compensating circuit, the TCXO is classified into a one-chip type TCXO using an integrated circuit (IC) chip, and a discrete type TCXO having components such as piezoelectric elements, integrated circuits, capacitors, inductors and resistive elements mounted thereon.
In general, although the discrete type TCXO is superior to the one-chip type TCXO in terms of phase noise characteristic, the discrete type TCXO is difficult to be made compact because it must contain various components. Accordingly, the discrete type TCXO is severely restricted in its adoption into a mobile communication terminal due to its large size, despite its excellent characteristics.
FIGS. 1a and 1b are a plan view and a side view showing a conventional discrete type TCXO 100. As shown in FIG. 1a, the discrete type TCXO 100 is configured to have a printed circuit board 101, a crystal package 103 mounted on the printed circuit board 101, and components 105 of a temperature compensating circuit arranged at both sides of the crystal package 103. As appreciated from FIG. 1b, the components 105 are positioned at a level lower than that of the crystal package 103.
The temperature compensating components 105 usually occupy an area 2 to 3 times as large as an area of the TCXO 100 (5.0xc3x973.2 mm2 or 4.7xc3x972.9 mm2). Consequently, the printed circuit board 101 incorporated in the TCXO requires an area far larger than that of the TCXO. Hence, an area of a finished product will also become large (for example, 7.0xc3x975.2 mm2).
As such, there is a considerable limitation to compactness of a conventional temperature compensated crystal oscillator because of a space required to accommodate the temperature compensating components. On this account, such a discrete type TCXO cannot be successfully adopted into mobile communication terminals.
Therefore, there has been strongly required a temperature compensated crystal oscillator and a method of manufacturing the same in the art, in which a space for accommodating temperature compensating components is minimized.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a temperature compensated crystal oscillator which is intended to achieve compactness of a product by making use of a bottom surface as an area for accommodating components.
Another object of the present invention is to provide a method of manufacturing the temperature compensated crystal oscillator.
In order to accomplish the above object, the present invention provides a temperature compensated crystal oscillator comprising: a crystal package including a package board and a crystal oscillating piece disposed on the package board; first and second conductive patterns formed on a surface of the package board; components for constituting a temperature compensating circuit, which are disposed at the first conductive patterns within a component mounting area defined by the first conductive patterns; exterior terminals disposed at the second conductive patterns within terminal forming areas defined by the second conductive patterns; and a resin molded part formed on the surface of the package board for protecting the temperature compensating components.
In an embodiment of the present invention, each of the exterior terminals may be formed to have a rectangular shape in transverse section, so that the surface of the package board except for the exterior terminals assumes a cruciform shape in plan.
In another embodiment of the present invention, each of the exterior terminals may be formed to have a triangular shape in transverse section, so that the surface of the package board except for the exterior terminals assumes an octagonal shape in plan. According to this embodiment, it is possible to provide a surface of a package board with a relatively large area required for mounting of components.
Furthermore, to more efficiently use the surface of the package board, at least one of the temperature compensating components is preferably disposed between two exterior terminals formed at either one of the four sides of the package board.
In a further preferable embodiment, the exterior terminals may be shaped such that a height thereof is equal to or larger than a height of the highest component, and the resin molded part may be molded such that the exterior terminals are exposed at ends thereof and the components are completely enveloped by the resin molded part.
In addition, the present invention provides a method of manufacturing a temperature compensated crystal oscillator comprising the steps of: preparing a crystal package including a package board and a crystal oscillating piece disposed on the package board; forming first and second conductive patterns on a surface of the package board; placing components for constituting a temperature compensating circuit at the first conductive patterns within a component mounting area defined by the first conductive patterns; forming exterior terminals at the second conductive patterns within terminal forming areas defined by the second conductive patterns; and molding the surface of the package board with resin material for protecting the temperature compensating components.